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Transition (genetics)

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Not to be confused with the evolutionary concept of a transitional fossil.

In genetics, a transition is a mutation changing a purine to another purine nucleotide (A <-> G) or a pyrimidine to another pyrimidine nucleotide (C <-> T). Approximately two out of every three single nucleotide polymorphisms (SNPs) are transitions.

They can be caused by oxidative deamination and tautomerization.^[1]

5-Methylcytosine is more prone to transition than unmethylated cytosine, due to spontaneous deamination.